26 Jan
2009
26 Jan
'09
10:50 p.m.
James Cameron says:
Undervolt of fan can be risky. Check the specifications of the fan to
ensure it is designed to start even at 5V.
Thanks for bringing this up.
A few years back I did a lot of under-voltage fan testing and came to the same conclusions
as James stated.
In the end I started to select good fans and ran them at 8 volts via a 7808 regulator
mounted on the inside of the case. All that's needed is the regulator chip, two small
bypass caps soldered from each of the business ends to the central ground pin, and the
wires from the power supply and to the fan(s). The chip can be mounted right on the case
with no insulator, because the "tab" is at ground potential.
I even experimented with using adjustable regulators where I would use a potentiometer to
adjust the voltage from 5 to 10.2 volts for the fans. I mounted those "pots"
through a hole in the back of the case a couple of times, put knobs on them, and called
them the computer "volume control". I'm sure that a better way I could have
done it is with a thermostatic feedback circuit, but that's for another time.